简单实现聊天功能：

必须客户端先发消息。

服务器端：

package com.robert.view;import java.io.BufferedInputStream;import java.io.BufferedOutputStream;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;import java.util.Scanner;import com.robert.view.CustomerClient.ReadThreadHandler;public class ServerClient {	ServerSocket serverSocket = null;	Socket clientSocket = null;	Socket socket = null;	InputStream inputStream = null;	BufferedInputStream bis = null;	DataInputStream dis = null;	OutputStream outputStream = null;	BufferedOutputStream bos = null;	DataOutputStream dos = null;	public static void main(String[] args) {		ServerClient serverClient = new ServerClient();		serverClient.communicate();	}	public void communicate() {		try {			serverSocket = new ServerSocket(9999);			while (true) {				socket = serverSocket.accept();				Runnable threadHandler = new ThreadHandler(socket);				Thread thread = new Thread(threadHandler);				thread.start();				Runnable readThreadHandler = new ReadThreadHandler(socket);				Thread readThread = new Thread(readThreadHandler);				readThread.start();			}		} catch (IOException e) {			e.printStackTrace();		}	}	class ThreadHandler implements Runnable {		private Socket socket;		public ThreadHandler(Socket socket) {			this.socket = socket;		}		@Override		public void run() {			try {				String input = "";				while (!"exit".equals(input)) {					outputStream = socket.getOutputStream();					bos = new BufferedOutputStream(outputStream);					dos = new DataOutputStream(bos);					Scanner scanner = new Scanner(System.in);					input = scanner.nextLine();					dos.writeUTF(input);					dos.flush();				}			} catch (IOException e) {				e.printStackTrace();			}		}	}	class ReadThreadHandler implements Runnable {		private Socket socket = null;		public ReadThreadHandler(Socket socket) {			this.socket = socket;		}		@Override		public void run() {			try {				String output = "";				while(!"exit".equals(output))				{					inputStream = socket.getInputStream();					bis = new BufferedInputStream(inputStream);					dis = new DataInputStream(bis);					output = dis.readUTF();					System.out.println("client:"+output);					}							} catch (IOException e) {				e.printStackTrace();			}		}	}}

客户端：

package com.robert.view;import java.io.BufferedInputStream;import java.io.BufferedOutputStream;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;import java.net.UnknownHostException;import java.util.Scanner;public class CustomerClient {	OutputStream outputStream = null;	BufferedOutputStream bos = null;	DataOutputStream dos = null;	InputStream inputStream = null;	BufferedInputStream bis = null;	DataInputStream dis = null;	public static void main(String[] args) {		CustomerClient customerClient = new CustomerClient();		customerClient.communication();	}	public void communication() {		try {			Socket socket = new Socket("localhost", 9999);			Runnable writeThreadHandler = new WriteThreadHandler(socket);			Thread writeThread = new Thread(writeThreadHandler);			writeThread.start();			Runnable readThreadHandler = new ReadThreadHandler(socket);			Thread readThread = new Thread(readThreadHandler);			readThread.start();		} catch (UnknownHostException e) {			e.printStackTrace();		} catch (IOException e) {			e.printStackTrace();		}	}	class WriteThreadHandler implements Runnable {		Socket socket = null;		public WriteThreadHandler(Socket socket) {			this.socket = socket;		}		@Override		public void run() {			try {				String input = "";				while (!"exit".equals(input)) {					outputStream = socket.getOutputStream();					bos = new BufferedOutputStream(outputStream);					dos = new DataOutputStream(bos);					Scanner scanner = new Scanner(System.in);					input = scanner.nextLine();					dos.writeUTF(input);					dos.flush();				}			} catch (IOException e) {				e.printStackTrace();			}		}	}	class ReadThreadHandler implements Runnable {		private Socket socket = null;		public ReadThreadHandler(Socket socket) {			this.socket = socket;		}		@Override		public void run() {			try {				String output = "";				while (!"exit".equals(output)) {					inputStream = socket.getInputStream();					bis = new BufferedInputStream(inputStream);					dis = new DataInputStream(bis);					output = dis.readUTF();					System.out.println("server:" + output);				}			} catch (IOException e) {				e.printStackTrace();			}		}	}}

实现原理：

1.先建立一个Server端，然后客户端去连接该server。

2.取得对应端（server端，client端）的输入流和输出流。

3.发送消息，互相通信。